According to the variable valve timing control apparatus, a rotational phase of a driven side rotation member relative to a driving side rotation member can be varied towards an advancing angle side by draining a fluid in a retarded angle chamber while incrementing a volume of an advanced angle chamber by a pressurized fluid supplied to an advanced angle fluid passage, and the rotational phase can be varied towards a retarded angle side by draining the fluid in the advanced angle chamber while incrementing a volume of the retarded angle chamber by the pressurized fluid supplied to a retarded angle fluid passage. Further, for example, the rotational phase of the driven side rotation member relative to the driving side rotation member can be locked at an intermediate phase between a most retarded angle phase and a most advanced angle phase so that an opening and closing timing of an intake valve or an exhaust valve is assumed to be an optimum timing for starting an engine.
JP2010-223172A discloses a variable valve timing control apparatus in which three fluid passages each supplying a pressurized fluid to an advanced angle fluid passage, a retarded angle fluid passage, and a lock fluid passage provided at a driven side rotation member are open to a fixed peripheral surface of a fixed member sliding relative to a rotational peripheral surface of the driven side rotation member. In a case where the pressurized fluid supplied from the fluid passages leaks via a sliding surface between the rotational peripheral surface and the fixed peripheral surface, there is a possibility that a switching operation of a lock member and a change in a valve opening-closing timing cannot be performed at an appropriate timing. Accordingly, it is necessary to machine process the rotational peripheral surface and the fixed peripheral surface with high precision so as not to cause leakages of the fluid via the sliding surface, which is likely to increase manufacturing costs.
JP3986331B discloses a variable valve timing control apparatus which includes an advanced angle fluid passage and a retarded angle fluid passage provided at a driven side rotation member and two fluid passages each supplying a pressurized fluid to the advanced angle fluid passage and the retarded angle fluid passage. The advanced angle fluid passage and the retarded angle fluid passage are in communication with two fluid passages each supplying the pressurized fluid to the advanced angle fluid passage and the retarded angle fluid passage, respectively, via a communication portion for retarded angle and a communication portion for advanced angle, respectively, which are formed annularly by dividing a void between the rotational peripheral surface of the driven side rotation member and the fixed peripheral surface of the fixed member by means of seal rings. Thus, leakages of the fluid provided between the rotational peripheral surface and the fixed peripheral surface can be prevented by the seal ring without machining the rotational peripheral surface and the fixed peripheral surface with high precision, that is, while adopting a structure which is unlikely to increase manufacturing costs.
Here, it is considered to establish a communication between each of the advanced angle fluid passage, the retarded angle fluid passage, and the lock fluid passage and each of three fluid passages for supplying the pressurized fluid to the advanced angle fluid passage, the retarded angle fluid passage, and the lock fluid passage, respectively, via a communication passage for advanced angle, a communication passage for retarded angle, and a communication passage for lock which are formed by annularly dividing a void provided between a rotational peripheral surface and a fixed peripheral surface by means of seal rings for the variable valve timing control apparatus disclosed in JP2010-223172A in order to perform the switching operation of the lock member and to change in the valve opening-closing timing at appropriate timing while adopting a structure which is unlikely to increase manufacturing costs.
However, for example, provided that the communication portion for lock is positioned between the communication portion for advanced angle and the communication portion for retarded angle, the sealing dividing, or defining the communication portion for lock and the communication portion for advanced angle, and the seal ring dividing, or defining the communication portion for lock and the communication portion for retarded angle may be deformed and damaged.
That is, when the pressurized fluid is supplied to the advanced angle fluid passage or the retarded angle fluid passage in a state where the pressurized fluid is not supplied to the lock fluid passage, the seal ring is urged to displace towards the communication portion for lock by a fluid pressure in the communication portion for advanced angle or in the communication portion for retarded angle. Further, when the pressurized fluid is supplied to the lock fluid passage in a state where the pressurized fluid is not supplied to the advanced angle fluid passage and the retarded angle fluid passage, the seal ring is urged to displace towards the communication portion for advanced angle or the communication portion for retarded angle by the fluid pressure in the communication portion for lock. Still further, even when the pressurized fluid is simultaneously supplied to the advanced angle fluid passage or the retarded angle fluid passage, and to the lock fluid passage by a common fluid pump, there is a case that fluid pressure level between the communication portion for advanced angle or the communication portion for the retarded angle and the communication portion for lock slightly differ from each another due to differences in pressure loss, and the seal ring is urged to displace towards the communication portion for advanced angle or the communication portion for retarded angle, or towards the communication portion for lock in response to the pressure difference therebetween.
Because flexural rigidity of the seal ring in a rotational axis direction is not necessarily even because of slight dispersion of machining precision and an accuracy of dimension along a circumferential direction of the seal ring, the displacement of the seal ring is assumed to be uneven in the circumferential direction, and may be increased within a particular range in the circumferential direction. Because the supply of the pressurized fluid to the advanced angle fluid passage or the retarded angle fluid passage and the supply of the pressurized fluid to the lock fluid passage are repeated as necessity arises, the seal ring may eventually be damaged by fatigue because of deformation.